Re: [TCML] NST Insulator Carbon Track

[bartb <bartb@xxxxxxxxxxxxxxxx>]

I worded that poorly. It's not that it needs to cool quickly, but 
uniformly across the thickness of the wax. When I covered the wax with 
the lid the result was worse than when I let it cool with the lid off. 
Leaving the lid on, I "theorize" allowed the area around the case 
(sinked) to cool quicker than the center. However, with the lid off the 
wax allowed the center to cool at a rate similar to the surrounding case 
(uniformly).

The main point was to layer the wax and let each layer cool. This will 
allow the wax to cool uniformly throughout. I suspect your experience 
and my own are probably a little different based on maybe the amount of 
wax we are pouring in at any given stage or maybe even outside 
temperatures. However, I have even poured the wax in about half full and 
let it cool only during the time it took to melt the rest of the wax on 
the stove (which I then poured to top off the case). I've had better 
luck with the lid off as far as preventing caverns. But I then realized 
I should probably just pour a little in at a time to allow the wax to 
cool faster and uniformly (faster meaning less wax to cool) to prevent 
caverns and even to prevent the center from drooping inward.

Take care,
Bart



Quarkster wrote:
> Bart -
>
> Why does the wax potting compound "need to cool quickly"?
>
> My experience has been just the opposite, where a slow cooling rate 
> allows more uniform shrinkage distributed all across the mass of  wax, 
> while rapid cooling tends to cause very deep "sinks"or even hidden 
> voids at the center of the mass of wax.
>
> Regards,
> Herr Zapp
>
> ----- Original Message ----- From: "bartb" <bartb@xxxxxxxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Monday, April 13, 2009 6:06 PM
> Subject: [TCML] NST Insulator Carbon Track
>
>
> > Hi All,
> >
> > A couple weeks ago I mentioned depotting my NST, etc.. Well it worked 
> > for a moment and died. One side of secondary was at 0V (again). 
> > Scratched my head then once again melted out the wax and put the core 
> > on my work bench. All was good on the work bench. Put it back in the 
> > case and all was bad.. I had new 15kV GTO wire, so I knew that should 
> > be good. It had to be the insulator to case. I pulled out the 
> > insulator a few inches and tested. Sure enough, the NST was good again.
> >
> > Apparently, this insulator has a carbon track. I never expected that 
> > to happen, yet it did. Just wanted to let you know this particular 
> > saga since others may experience this at some point.
> >
> > BTW, if using wax for a potting compound as I do, to prevent air 
> > bubbles (and sometimes deep caverns), never pour a gallon of wax into 
> > the case. You have to layer the wax. I use 1/2" increments letting 
> > the wax harden before adding more wax. Also, never put the lid on the 
> > case when letting the wax cool (it needs to cool quickly).
> >
> > I'm unfortunately getting really good at potting and depotting this 
> > particular NST.
> >
> > Take care,
> > Bart
> > _______________________________________________
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> > Tesla@xxxxxxxxxxxxxx
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>
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